The disclosure relates generally to power systems and methods that employ generators for backup power to a facility, and more particularly, to a system, method, and controller for optimizing a generator start delay and runtime following an outage.
Typically, electrical power is provided from a primary source (such as a utility or a “grid”) to facilities that include residential, small business, and industrial environments. However, occasionally the electrical power is interrupted for reasons that may include weather damage to power lines and equipment, power plant shutdowns (scheduled or not), and other sorts of system failures such as cascading plant failures. Although the grid can be generally stable over time and may operate uninterrupted for months or more, the possibility of lost power from the primary source is nevertheless ever-present and can result in a range of hardships that extend from an inconvenience, to lost business, to life-threatening situations.
For instance, in a residential application, not only are the occupants inconvenienced, but if sump pumps, refrigerators, furnaces, and air conditioning units are not powered, this can lead to flooding in the basement, food spoilage, high temperatures within the residence during summer (e.g., stagnant hot temperatures), or dangerously low temperatures during the winter (e.g., for certain medical conditions, threat of burst water lines, risk of frostbite). A business as well, such as a restaurant, may experience food spoilage and customer dissatisfaction in the event of a power outage. In an industrial setting, if power is lost, a plant shutdown may occur that can lead to lost production and employee/equipment downtime, and some industrial facilities have a critical requirement for continuous power (such as certain plant processes, computer installations, and the like), such as a wastewater treatment plant in which a power loss can lead to overflowing tanks and untreated sewage discharge. Also, some facilities such as urgent care providers and hospitals rely on uninterrupted power to power life-supporting equipment. In many instances there is a legal requirement to provide uninterrupted, or minimally interrupted, power to the facility to avoid the repercussions that can occur if primary power is lost.
As such, backup electrical generators are often provided that serve as a standby or secondary source in the event of primary power outage. The backup generator may be manually connected to loads within the facility when primary power is lost. Or, in many instances a backup system includes an automatic transfer switch (ATS) that detects power from the primary source, and when primary power is lost, the ATS controllably disconnects the primary source, powers up the standby generator, and engages the generator power with the loads. The ATS can work in reverse as well, so that when primary power is again online the ATS switches back to the primary and powers down the standby generator.
ATS' often have built-in time delays that are implemented during operation to ensure the least amount of interruption to the end user. In one example, there may be a time delay to prevent automatic re-closures from occurring before the ATS starts the generator, which protects against un-needed engine starts. Another example of a time delay is the time delay before transferring to the generator once the generator is running, which allows for proper engine warm-up before applying a load to it. And, another time delay is the time that the generator runs after it has been determined to shut down the generator and after the generator load has been removed (that is, to run in an unloaded state and cool the generator). ATS' typically have timers that are either hard coded and cannot be changed, dip switches that allow minimal choices in the time delay, or the time delay may be programmed in advance.
When an outage occurs in, for instance, a residence or a small business such as a restaurant, a controller or the ATS is typically programmed to start and connect the generator within a short period of time after the outage occurs. After starting the generator, it runs essentially 100% of the time. As such, the numerous types of loads within the facility (e.g., refrigerator, air conditioner, freezer, furnace, computer, stove, oven, entertainment systems, etc.) are kept powered and occupants of the facility experience minimal downtime and inconvenience.
However, because of the automated system operation of the ATS, generator backup is provided also for times when an outage occurs and the facility is unoccupied. For instance, if the facility is a residence and the occupants are on vacation, then the load requirements are not as stringent as compared to when occupied. Similarly, if the facility is a small business such as an office complex or a restaurant (typically unoccupied late evening or early morning), there may be less stringent requirements for running the loads therein.
For instance, according to the USDA, with doors kept closed, refrigerators can maintain a safe temperature for 4 hours, while freezers can maintain proper temperatures for up 24 hours or more (depending on how full the freezer is). As another example, an unoccupied building may only need to be kept above freezing in winter, or below a certain temperature in summer (such as for plants within the residence), and not to the comfort level kept typically while occupied.
Thus, it may not be necessary to continually run the generator and power the loads within the facility if it is unoccupied. As one example, by continually running the refrigerator and having it cycle on and off based on its normal operating parameters. And, in another example, by continually running the air conditioner (or furnace) and having it cycle on and off based on its normal operating parameters, the generator may thereby be running excessively.
Therefore, when a facility is unoccupied, it is desirable to control the loads within a facility in a different fashion than when it is occupied and when the facility is under backup generator power.